How To Keep Up With Comet Siding Spring's Encounter with Mars Tomorrow

Comet Siding Spring will make a close pass of the planet Mars tomorrow (Sunday, October 19) while human and robotic observers watch intently to see what they can learn about this rather rare type of celestial body.  On Earth, the best viewing is from the Southern Hemisphere and it will not be visible to the naked eye (Magnitude 13), but several websites plan live coverage with images and/or commentary.

Astronomers world-wide have been eagerly awaiting the arrival of Comet Siding Spring, also known as C/2013 A1, which was discovered in January 2013 by Robert McNaught at the Siding Spring Observatory in Australia.   This particular type of comet, from the Oort Cloud far beyond the orbit of Pluto, rarely reaches the inner solar system.  This is the comet’s first time sweeping around the Sun so none of its material has yet been affected by the Sun’s heat.  It is comprised of material from the time the solar system was formed 4.6 billion years ago.

The nucleus of the comet will come within 87,000 miles (140,000 kilometers) of the surface of Mars at 2:28 pm Eastern Daylight Time (11:28 am PDT, 18:28 GMT).   It will pass Mars traveling at 126,000 miles per hour (56 kilometers per second). 

Five spacecraft are currently orbiting Mars:  three from NASA and one each from the European Space Agency (ESA) and the Indian Space Research Organization (ISRO).  In addition, two functioning NASA rovers are on the surface:  Opportunity and Curiosity.  All will be tasked to study the comet and its interaction with Mars. 

To be on the safe side, NASA positioned its orbiters — Mars Odyssey, Mars Reconnaissance Orbiter, and MAVEN — so they will be on the opposite side of the planet as the comet’s tail passes by lest any of the particles damage spacecraft instruments.   ISRO similarly repositioned its Mars Orbiter Mission (MOM).  The European Space Agency decided that the risk of damage to its Mars Express orbiter was so low that it did not change its orbit.   The tail will be in close proximity to Mars about 90 minutes after the nucleus goes by and will be there for only about 20 minutes.

Many other space- and Earth-based observatories will study the comet as well.   NASA has a website with a wealth of information about its plans.

Comet expert Karl Battams posted an analysis of the parallels between observing this comet and last year’s comet ISON, which was a disappointment for many observers because the comet was not as spectacular as expected.  Today Battams said in his blog post that the same phenomenon has occurred with Comet Siding Spring:  “…again, like comet ISON – we have watched nervously in these final couple of weeks … as the comet has suddenly and dramatically faded in brightness.  This in particular has left us scratching our collective heads….”   Still, although “we have plenty of unknowns,” he is optimistic for a successful Mars-based observing campaign.

He (@SungrazerComets) and the Planetary Society’s Emily Lakdawalla (@elakdawalla) are among those who will be tweeting the event (#MarsComet or #SidingSpring).  Both list places on the web that will have live images and/or commentary:

• Virtual Telescope beginning at 16:45 GMT (12:45 pm EDT)
• ESA beginning at 1:50 pm EDT
• Slooh beginning at 2:15 pm EDT
• amateur astronomer Peter Lake will broadcast from the iTelescope.net Observatory at Siding Spring